Several apps create products, variants or change pricing. The offers must first be stopped in the app, ensure you wait for the offers to finish updating. Depending on the number of products that need to be updated, it can take a few minutes or several hours to complete.

No, the liquid code added to the theme files is not automatically removed. The code that was installed for this app to work only applies to the app so you can leave it in and your store will run just fine. If you ever decide to install it again you won't need to redo the liquid install.